How can court surface affect service speeds? Are you kidding me? On a fast slick grass court, everyone TRIES to serve fast, both serves. On the roughest, slowest, tackiest, wettest clay court, you might hit some flat fast ones once in a while, but you know they won't be very effective, and no reason to risk your second serve by pushing into the 100's, so you slow that serve way down. You gotta know that, if you play tennis.